Circuit for dissipating the potential induced in each phase winding of a cycloconverter operated motor upon termination of conduction therethrough

ABSTRACT

A circuit for dissipating the potential induced in each phase winding of a cycloconverter operated alternating current motor upon the termination of conduction therethrough. The anodecathode electrodes of each of two oppositely poled silicon controlled rectifiers are connected in series with a respective parallel combination of a resistor and a capacitor across each phase winding of the motor. When conduction through each phase winding in either direction is to be terminated, a gate signal is produced and applied across the gate-cathode electrodes of the one of the silicon controlled rectifiers connected across the phase winding through which conduction is to be terminated which is forward poled by the potential induced in the phase winding as the magnitude of phase current flow therethrough decreases.

United States Patent Sawyer et al. [451 Aug. 15, 1972 [54] CIRCUIT FORDISSIPATING THE 3,617,838 1l/l971 Brandt ..318/227 POTENTIAL INDUCED INEACH 3,624,472 11/1971 Graham ..318/227 PHASE WINDING OF ACYCLOCONVERTER OPERATED Primary Examiner-Gene Z. Rubinson MOTOR UPONTERMINATION ()F Attorney-Eugene W. Christen et a1. CONDUCTIONTHERETI'IROUGH 5 CT [72] Inventors: Elbert M. Sawyer, Torrance, Calif.;I 7] ABSTRA William M. Haas, Anderson, 1nd. A circuit for dissipatingthe potential induced in each phase winding of a cycloconverter operatedaltemat- [73] Asslgnee' ga s t r Corporation ing current motor upon thetermination of conduction 1 therethrough. The anode-cathode electrodesof each [22] F lied: July 2, 1971 of two oppositely poled siliconcontrolled rectifiers are [21] AppL NOJ 159,228 connected in series witha respective parallel combinatron of a resistor and a capacitor acrosseach phase winding of the motor. When conduction through each U-S. 3 I6, phase in either direction is to be terminated 8 318/231 321/5 321/69gate signal is produced and applied across the gate- [51] Illt. Ci..1102 5/49 cathode electrodes of the one of the silicon controlled [58]held of Search 318/221 231; 321/5 rectifiers connected across the phasewinding through 3 17/ 6 which conduction is to be terminated which isforward poled by the potential induced in the phase winding as [56] mcltgd the magnitude of phase current flow therethrough UNITED STATESPATENTS decreases- 3,603,866 9/1971 Opal ..318/227 4 Claims, 5 DrawingFigures SCR GATE SWITCH SQUARE WAVE RAT

SCR

GATE

SWITCH SCH GAI'L SWITCH SCR GATE SWlTCH SCF\ GATE

bCR GATE SWI l'CH il'Ei SOURCE SCH GATE SWXTCH SQUAR E WA E TO RPATENTEDAUB 1 5 1912 3,684,935

I! SQUARE J scR vvAvE GATE GENERATOR HSWITCH jig SCR GATE SWITCH sGR Z9GATE 1; 7

I SCR GATE SWITCH 19 Nfl A A.C. i \C-QPOTENUAL GVATE p SOURCE SCR k sITCH N GATE 585.9 541 SWITCH 20 sGR .95 GATE 2 SWITCH \IZ/ i t/16? 6;???GENERATOR JL' ASWITCH,

CURRENT CURRENT SlLlCON coNTRoLED RECTIFIERS l3, /5

ATTORNEY SILICON CONTROLLED RECTlFiER 4/0 1 GATE SIGNAL FOR h CIRCUITFOR DISSIPATING THE POTENTIAL INDUCED IN EACH PHASE WINDING OF ACYCLOCONVERTER OPERATED MOTOR UPON TERMINATION OF CONDUCTIONTHERETHROUGH The invention herein described was made in the course ofwork under contract or subcontract thereunder with the Department ofDefense.

This invention is directed to a circuit for dissipating the potentialinduced in each phase winding of a cycloconverter operated motor uponthe termination of conduction therethrough.

In cycloconverter systems for cyclically energizing the phase windingsof an alternating current motor from an alternating current supplypotential source, each phase of the supply potential source suppliescurrent to each phase winding of the motor in a first direction througha cycloconverter silicon controlled rectifier and in a second oppositedirection through another oppositely poled cycloconverter siliconcontrolled rectifier. Consequently, for each phase of the alternatingcurrent supply potential source, there is a corresponding cycloconvertersilicon controlled rectifier having the cathode electrode connected toone terminal end of each phase winding of the motor through whichcurrent is supplied thereto in a first direction and a correspondingcycloconverter silicon controlled rectifier having the anode electrodeconnected to the same terminal end of each phase winding of the motorthrough which current is supplied thereto in a second oppositedirection. For example, with a three-phase cycloconverter system inwhich a three-phase altemating current motor is supplied from athree-phase supply potential source, the cathode electrode of each ofthree cycloconverter silicon controlled rectifiers, generally termed thecommon cathode group, and the anode electrode of each of three othercycloconverter silicon controlled rectifiers, generally termed thecommon anode group, are connected to the same terminal end of each phasewinding of the motor. In operation, gate signals are simultaneouslyapplied across and removed from the gate-cathode electrodes of all ofthe cycloconverter silicon controlled rectifiers of each group.

One factor which limits the amount of current supplied the motor, thusthe torque produced by the motor, with cycloconverter systems is theenergy stored in each phase winding of the motor at the time conductiontherethrough is terminated. As the current supplied a phase winding ofthe motor begins to decrease when the alternating current supplypotential magnitude decreases toward zero, the inductance of the phasewinding tends to maintain phase current flow in the same direction. Thiswill cause the phase current to continue to flow in the same directioneven though the supply potential across the anode-cathode electrodes ofthe cycloconverter silicon controlled rectifier through which phasecurrent is supplied is of a polarity which would normally commutate thecycloconverter silicon controlled rectifier OFF because the potentialinduced in the phase winding controls the net cycloconverter siliconcontrolled rectifier potential until the energy stored in the phasewinding has decreased to a low value. At the conclusion of theconduction period through the group of cycloconverter silicon controlledrectifiers through which current is being supplied, this delay of thedecay or fall or phase current, which may continue for several cycles ofthe supply potential depending upon the magnitude of the energy storedin the motor phase winding, delays the actual tum-off of the lastconducting cycloconverter silicon controlled rectifier of the group atthe time the gate signals are removed. Consequently, this device willcontinue to conduct until the energy stored in the phase winding of themotor has been dissipated. If this stored energy causes the phasecurrent to persist, or hang on long enough, a line-to-line short, orfault, will be produced thereby at the point when the gate signals areapplied across the gate-cathode electrodes of the cycloconverter siliconcontrolled rectifiers of the group through which current is supplied inthe opposite direction to that phase winding of the motor. To preventthe energy stored in each phase winding of the motor from causing acycloconverter silicon controlled rectifier to hang on and create aline-to-line fault, it is necessary to accelerate the decay of phasecurrent in each motor phase winding. This may be accomplished bydissipating the potential induced in each phase winding of the motorupon the termination of conduction therethrough. By rapidly dissipatingthis induced potential through the circuit of this invention, themaximum motor current and, consequently, the maximum motor torque, maybe significantly increased without resulting in a line-to-line fault dueto motor phase current persisting to or beyond the 180 point.

It is, therefore, an object of this invention to provide a circuit fordissipating the potential induced in each phase winding of acycloconverter operated motor upon the termination of conductiontherethrough.

In accordance with this invention, a circuit for dissipating thepotential induced in each phase winding of a cycloconverter operatedalternating current motor upon the termination of conductiontherethrough is provided wherein the anode-cathode electrodes of each oftwo oppositely poled silicon controlled rectifiers are connected inseries with a respective parallel combination of a resistor and acapacitor across each phase winding of the motor and a gate signal,produced when conduction through each phase winding in either directionis to be terminated, is applied across the gate-cathode electrodes ofthe one of the silicon controlled rectifiers connected across the phasewinding of the motor through which conduction is to be terminated whichis forward poled by the potential induced in the phase winding ascurrent flow therethrough decreases.

For a better understanding of the present invention, together withadditional objects, advantages and features thereof, reference is madeto the following description and accompanying drawings in which:

FIG. 1 sets forth a typical cycloconverter system for cyclicallyenergizing the phase windings of a threephase, alternating current motorfrom a three-phase, alternating current supply potential source in blockform with the circuit of this invention incorporated therein and setforth in schematic form.

FIGS. 20, 2b, 2c and 2d are curves useful in understanding the circuitof FIG. 1.

Referring to FIG. 1 of the drawings, a typical cycloconverter system forcyclically energizing the phase windings of a three-phase, alternatingcurrent motor 30, having three wye" connected phase windings 30a, 30b,and 30c and a rotor 31, from a three-phase, alternating current supplypotential source 19, is set forth in block form. As the alternatingcurrent supply potential source may be any one of several well known inthe art and, per se, forms no part of this invention, it has beenindicated in FIG. 1 in block form. Phase windings 30a, 30b and 30c ofmotor 30 are cyclically energized through a cycloconverter circuit madeup of a network of 18 silicon controlled rectifiers, referenced by thenumerals 1 through 18, inclusive. Corresponding to each cycloconvertersilicon controlled rectifier is a cycloconverter silicon controlledrectifier gate switch for producing a gate signal. In the interest ofreducing drawing complexity, only six cycloconverter silicon controlledrectifier gate switches which correspond to respective cycloconvertersilicon controlled rectifiers through are shown in block form in FIG. 1and referenced by the numerals through 25. Any one of the siliconcontrolled rectifier gate switches well known in the art which producean output potential signal may be employed as these cycloconvertersilicon controlled rectifier gate switches which, per se,'form no partof this invention. So that cycloconverter silicon controlled rectifiergate signals may be applied to the proper cycloconverter siliconcontrolled rectifiers at the proper time, a rotor position sensor may beemployed. The rotor position sensor may be of the type shown in theUnited States patents to Campbell et al., U.S. Pat. No. 3,320,565, andHuntzinger et al. U.S. Pat. No. 3,395,328, or to Kirk, U.S. Pat. No.3,483,458, all of which are assigned to the assignee of thisapplication. As the rotor position sensor, per se, forms no part of thisinvention, it has been illustrated in FIG. 1 in block form andreferenced by the numeral 32. The output signal of each of the rotorposition sensors may be applied to a respective square wave generatorwhich may be conventional bistable multivibrator circuits which convertthe rotor position sensor pulse into a square wave-form. The two squarewave generators corresponding to the respective rotor position sensorsfor phase winding 30a are shown in 7 block form in FIG. 1 and referencedby the numerals 33 and 34. Any bistable multivibrator circuit well knownin the art may be employed as these square wave generators which, perse, form no part of this invention. The output of the square wavegenerators is applied to the six cycloconverter silicon controlledrectifier gate switches which correspond to the cycloconverter siliconcontrolled rectifiers through which motor phase winding 30a isenergized. That is, the output of square wave generator 33 is applied tothe cycloconverter silicon controlled rectifier gate switches 20, 21 and22 which correspond to common anode group cycloconverter siliconcontrolled rectifiers 10, 11 and 12, respectively, and the output ofsquare wave generator 34 is applied to the cycloconverter siliconcontrolled rectifier gate switches 23, 24 and 25 which correspond tocommon cathode group cycloconverter silicon controlled rectifiers 13, 14and 15, respectively. With this arrangement, all of the cycloconvertersilicon controlled rectifiers of the common anode group aresimultaneously triggered and all of the cycloconverter siliconcontrolled rectifiers of the common cathode group are simultaneouslytriggered.

In cycloconverter systems of this type, two square wave generators andsix cycloconverter silicon controlled rectifier gate switchesinterconnected as shown in FIG. 1 for phase winding 30a of motor 30 areemployed for each phase winding of the motor. As each of phase windings30b and 300 of motor 30 require the same number of square wavegenerators and cycloconverter silicon controlled rectifier gate switchesinterconnected the same way as for phase winding 30a, in the interest ofreducing drawing complexity, the details for motor phase windings 30band 300 are not set forth in FIG. 1.

Assume that the common cathode group of cycloconverter siliconcontrolled rectifiers l3, l4 and 15, connected to the tenninal end 35 ofphase winding 30a, are simultaneously gated ON by respectivecycloconverter silicon controlled rectifier gate switches 23, 24 and 25and are conducting in turn, depending upon which of the three is at themost positive supply potential. Phase current will flow into terminalend 35 of phase winding 30a toward the neutral point N. As the phasecurrent through phase winding 30a decreases over the last of thepositive half cycles of the supply potential, a potential is induced inphase winding 30a of a polarity relationship, neutral point N positivewith respect to terminal end 35, which will tend to maintain j phasecurrent flow in the same direction. Near the end of these half cycles,cycloconverter silicon controlled rectifier gate switches 23, 24 and 25remove the gate signals from respective cycloconverter siliconcontrolled rectifiers 13, 14 and 15. As each is commutated OFF by thesupply potential, the phase current will try to decrease at the samerate as the applied frequency. However, due to the energy stored in theinductance of phase winding 30a, the winding will produce a potentialdue to L di/dt of a polarity in the direction to maintain the flow ofphase current, positive at the neutral point N with respect to terminalend 35. This potential polarity is in the proper direction to maintainthe conduction of the cycloconverter silicon controlled rectifiers whichhave been conducting up to this instant. Two of the cycloconvertersilicon controlled rectifiers are off however, due to normal commutationafter gate removal, but the last cycloconverter silicon controlledrectifier still conducting will still conduct until the stored energy inthe motor phase winding 30a decays to a low value.

The circuit of this invention prevents this stored energy from causing acycloconverter silicon controlled rectifier to hang on and to eventuallycause a line-to-line fault, by dissipating the potential induced in thephase winding to accelerate the decay of the current in the phasewinding in a manner to be now explained.

In the cycloconverter system for cyclically energizing the phasewindings of an alternating current motor from an alternating currentsupply potential source of FIG. 1, the circuit of this invention fordissipating the potential induced in each phase winding of the motorupon the termination of conduction therethrough is schematically setforth in combination with the cycloconverter circuit through which thephase windings of the motor are energized and a cycloconverter siliconcontrolled rectifier gate switch for producing a gate signalcorresponding to each cycloconverter silicon controlled rectifierincluded in the network and comprises two silicon controlled rectifiers,each having anode, cathode and gate electrodes, two capacitors and tworesistors for each phase winding of the motor with the anode-cathodeelectrodes of one silicon controlled rectifier in series with theparallel combination of one of the capacitors and one of the resistorsand the anode-cathode electrodes of the other silicon controlledrectifier in series with the parallel combination of the other capacitorand the other resistor connected across each phase winding of the motorwith the silicon controlled rectifiers poled in an opposite polarityrelationship and means for producing a gate signal when conductionthrough each one of the phase windings of the motor is to be terminatedwhich are applied across the gate-cathode electrodes of the one of thesilicon controlled rectifiers connected across the phase winding of themotor through which conduction is to be terminated which is forwardpoled by the potential induced in the phase winding as the magnitude ofphase current flow therethrough decreases. Silicon controlled rectifier40 having the anode-cathode electrodes thereof in series with theparallel combination of capacitor 44 and resistor 45 is connected acrossphase winding 30a of motor 30 and silicon controlled rectifier 50 havingthe anodecathode electrodes thereof in series with the parallelcombination of capacitor 54 and resistor 55 is connected across phasewinding 30a of motor 30 with the silicon controlled rectifiers poled inan opposite polarity relationship. Both phase windings 30b and 300 havethis same circuitry connected thereacross.

To produce the gate signal when conduction through each one of the phasewindings of motor 30 is to be terminated, a silicon controlled rectifiergate switch corresponding to each phase winding of motor 30 forproducing a gate signal when conduction in a first direction through thephase winding of motor 30 to which it corresponds is to be terminatedand another silicon controlled rectifier gate switch corresponding toeach phase winding of motor 30 for producing a gate signal whenconduction in a second opposite direction through the phase winding ofmotor 30 to which it corresponds is to be terminated may be employed. Asthese silicon controlled rectifier gate switches may be any one of theseveral well known in the art and, per se, form no part of thisinvention, each has been illustrated in FIG. 1 in block form andreferenced by the numeral 46 and 56, respectively. The gate signalproduced by silicon controlled rectifier gate switch 46 is appliedacross the gate-cathode electrodes of the one of the silicon controlledrectifiers connected across the phase winding of the motor to which itcorresponds which is forward poled by the potential induced in the phasewinding as the magnitude of phase current flow in a first directiontherethrough decreases and the gate signal produced by siliconcontrolled rectifier gate switch 56 is applied across the gate-cathodeelectrodes of the one of the silicon controlled rectifiers connectedacross the phase winding of the motor to which it corresponds which isforward poled by the potential induced in the phase winding as themagnitude of phase current flow in a second opposite directiontherethrough decreases. Upon the termination of conduction through phasewinding 300 from terminal end 35 to neutral point N, the resultinginduced potential is of a positive polarity upon junction 47 withrespect to junction 57 and upon the termination of conduction throughphase winding 30a of motor 30 in a second opposite direction fromneutral point N toward terminal end 35, the resulting induced potentialis of a positive polarity upon junction 57 with respect to junction 47.Consequently, the gate signal produced by silicon controlled rectifiergate switch 46 is applied, through respective leads 48 and 49, acrossthe gate-cathode electrodes of silicon controlled rectifier 40 which isforward poled by the potential induced in phase winding 30a upon thetermination of conduction therethrough in a first direction fromterminal end 35 toward neutral point N and the gate signal produced bysilicon controlled rectifier gate switch 56 is applied, throughrespective leads 58 and 59, across the gate-cathode electrodes ofsilicon controlled rectifier 50 which is forward poled by the potentialinduced in phase winding 30a upon the termination of conductiontherethrough in a second opposite direction from neutral point N towardterminal 35.

Without intention or inference of a limitation thereto, siliconcontrolled rectifier gate switch 46 may produce a gate signal inresponse to each termination of the gate signal produced by any one ofthe cycloconverter silicon controlled rectifier gate switches 23, 24 or25 corresponding to the cycloconverter silicon controlled rectifiers l3,l4 and 15 which complete an energizing circuit in a first directionthrough phase winding 30a of motor 30 from terminal end 35 towardneutral point N. Silicon controlled rectifier gate switch 56 may producea gate signal in response to each termination of the gate signalproduced by any one of the cycloconverter silicon controlled rectifiergate switches 20, 21 or 22 corresponding to cycloconverter siliconcontrolled rectifiers 10, 11 and 12 which complete an energizing circuitin a second opposite direction through phase winding 30a of motor 30from neutral point N toward terminal end 35. In FIG. 1, siliconcontrolled rectifier gate switch 46 has been shown to be connected tothe output circuit of cycloconverter silicon controlled rectifier gateswitch 25 through leads 61 and 62 and silicon controlled rectifier gateswitch 56 has been shown to be connected across the output ofcycloconverter silicon controlled rectifier gate switch 20 through leads63 and 647 It is to be specifically understood that silicon controlledrectifier gate switch 46 may be connected across the output circuit ofeither of cycloconverter silicon'controlled rectifiers 23 or 24 and thatsilicon controlled rectifier gate switch 56 may be connected across theoutput circuit of either of cycloconverter silicon controlled rectifiergate switches 21 or 22.

Silicon controlled rectifier gate switches 46 and 56 may be conventionalmonostable multivibrator circuits with this arrangement of the typewhich are triggered to the alternate state upon the application of anegative going pulse to the input circuit thereof, in which state itremains for a period of time long enough to trigger the siliconcontrolled rectifier across the gate-cathode electrodes of which itsoutput signal is applied conductive.

Just prior to the termination of conduction through phase winding 30a ina first direction from terminal end 35 toward neutral point N, themagnitude of phase current flow therethrough decreases to induce apotential therein which forward poles silicon controlled rectifier 40.Consequently, the gate signal produced by silicon controlled rectifiergate switch 46 when conduction through phase winding 30a in a firstdirection is to be terminated triggers silicon controlled rectifier 40conductive through the anode-cathode electrodes thereof. The potentialinduced in phase winding 30a upon the termination of conduction in afirst direction therethrough charges capacitor 44. When capacitor 44 hasbecome charged, silicon controlled rectifier 40 extinguishes and thecharge upon capacitor 44 dissipates through resistor 45.

Just prior to the termination of conduction through phase winding 30a ofmotor 30 in a second opposite direction from neutral point N towardterminal end 35, the magnitude of phase current flow therethroughdecreases to induce a potential therein which forward poles siliconcontrolled rectifier 50. Consequently, the gate signal produced bysilicon controlled rectifier gate switch 56, when conduction throughphase winding 30a in the second opposite direction is to be terminated,triggers silicon controlled rectifier 50 conductive through theanode-cathode electrodes thereof. The potential induced in phase winding30a upon the termination of conduction in a second directiontherethrough charges capacitor 54. When capacitor 54 has become charged,silicon controlled rectifier 50 extinguishes and the charge uponcapacitor 54 is dissipated through resistor 55.

FIG. 2a illustrates the motor phase current of a cycloconverter operatedmotor without the circuit of this invention. The phase current risesrapidly to a maximum at which it levels. At the end of the desiredconduction angle, the gate signal is removed from the conductingcycloconverter silicon controlled rectifier supplying phase current tothe motor. The current decays to zero at nearly the 180 and 360 pointsand is modulated or rippled by the source alternator frequency. If thecurrent does not reach zero before the 180 and 360 points at which thecycloconverter silicon controlled rectifiers which supply current to thesame phase winding are gated ON, a line-to-line short circuit wouldoccur. FIG. 2b illustrates the motor phase current of a cycloconverteroperated motor with which the circuit of this invention is used. Forexample, the current through phase winding 30a is shown to increase fromzero toward a maximum value while the gate signal, curve 20, produced bythe cycloconverter silicon controlled rectifier gate switchcorresponding to any one of the cycloconverter silicon controlledrectifiers of the common cathode group for phase winding 30a is present.In response to the fall of this gate signal, silicon controlledrectifier gate switch 46 produces a gate signal, curve 2d, for siliconcontrolled rectifier 40. Conducting silicon controlled rectifier 40provides for the sharp decay of current through phase winding 30a tozero significantly before the polarity of the phase potential reversesat the 180 and 360 points, as shown in curve 2b, at which timecycloconverter silicon controlled rectifiers l0, l1 and 12 are gated ON.Consequently, the current of phase winding 30a is zero at the timecycloconverter silicon controlled rectifiers 10, 11 and 12 are gated ON,a condition which prevents a short circuit across any phase of thealternating current supply potential source 19.

While this description has been in reference to phase winding 30a ofmotor 30, the same circuitry and operation also applies to phasewindings 30b and 30c of motor 30.

While a preferred embodiment of the present invention has been shown anddescribed, it will be obvious to those skilled in the art that variousmodifications and substitutions may be made without departing from thespirit of the invention which is to be limited only within the scope ofthe appended claims.

What is claimed is:

1. In a cycloconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network-of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for eachsaid phase winding of said motor, two capacitors for each said phasewinding of said motor, two resistors for each said phase winding of saidmotor, means for connecting said anode-cathode electrodes of one of saidsilicon controlled rectifiers in series with the parallel combination ofone of said capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, means for producing a gate signal when conduction througheach one of said phase windings of said motor is to be tenninated, andmeans for applying said gate signal across said gate-cathode electrodesof the one of said silicon controlled rectifiers connected across thesaid phase winding of said motor through which conduction is to beterminated which is forward poled by the potential induced in the phasewinding as the magnitude of phase current flow therethrough decreases.

2. In a cycloconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for eachsaid phase winding of said motor, two capacitors for each said phasewinding of said motor, two resistors for each said phase winding of saidmotor, means for connecting said anode-cathode electrodes of one of saidsilicon controlled rectifiers in series with the parallel combination ofone of said capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, a silicon controlled rectifier gate switch for producing agate signal when conduction through each one of said phase winding ofsaid motor is to be terminated, and means for applying said gate signalacross said gatecathode electrodes of the one of said silicon controlledrectifiers connected across the said phase winding of said motor throughwhich conduction is to be terminated which is forward poled by thepotential induced in the phase winding as the magnitude of phase currentflow therethrough decreases.

3. In a cycloconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for eachsaid phase winding of said motor, two capacitors for each said phasewinding of said motor, two resistors for each said phase winding of saidmotor means for connecting said anode-cathode electrodes of one of saidsilicon controlled rectifiers in series with the parallel combination ofone of said capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, a first silicon controlled rectifier gate switchcorresponding to each said phase winding of said motor for producing agate signal when conduction in a first direction through the said phasewinding of said motor to which it corresponds is to be terminated, meansfor applying said gate signal produced by said first silicon controlledrectifier gate switch across said gatecathode electrodes of the one ofsaid silicon controlled rectifiers connected across the said phasewinding of said motor to which said first silicon controlled rectifiergate switch corresponds which is forward poled by the potential inducedin the phase winding as the magnitude of phase current flow in a firstdirection therethrough decreases, a second silicon controlled rectifiergate switch corresponding to each said phase winding of said motor forproducing a gate signal when conduction in a second opposite directionthrough the said phase winding of said motor to which it corresponds isto be terminated, and means for applying said gate signal produced bysaid second silicon con- Eli trolled rectifier gate switch across saidgate-cathode electrodes of the one of said silicon controlled rectifiersconnected across the said phase winding of said motor to which itcorresponds which is forward poled by the potential induced in the phasewinding as the mag nitude of phase current flow in a second oppositedirection therethrough decreases.

4. In a cycloconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for

g each said phase winding of said motor, two capacitors for each saidphase winding of said motor, two resistors for each said phase windingof said motor, means for connecting said anode-cathode electrodes of oneof said silicon controlled rectifiers in series with the parallelcombination of one of said capacitors and one of said resistors and forconnecting said anode-cathode electrodes of the other said siliconcontrolled rectifier in series with the parallel combination of theother said capacitor and the other said resistor across each said phasewinding of said motor with said silicon controlled rectifiers poled inan opposite polarity relationship, a first silicon controlled rectifiergate switch corresponding to each said phase winding of said motor forproducing a gate signal in response to each termination of the gatesignal produced by any one of the said cycloconverter silicon controlledrectifier gate switches corresponding to the said cycloconverter siliconcontrolled rectifiers which complete an energizing circuit in a firstdirection through the said phase winding of said motor to which itcorresponds, means for applying said gate signal produced by said firstsilicon controlled rectifier gate switch across said gate-cathodeelectrodes of the one of said silicon controlled rectifiers connectedacross the said phase winding of said motor to which it correspondswhich is forward poled by the potential induced in the phase winding asthe mag nitude of phase current flow in a first direction therethroughdecreases, a second silicon controlled rectifier gate switchcorresponding to each said phase winding of said motor for producing agate signal in response to each tennination of the gate signal producedby any one of the said cycloconverter silicon controlled rectifier gateswitches corresponding to the said cycloconverter silicon controlledrectifiers which complete an energizing circuit in a second oppositedirection through the said phase winding of said motor to which itcorresponds, and means for applying said gate signal produced by saidsecond silicon controlled rectifier gate switch across said gate-cathodeelectrodes of the one of said silicon controlled rectifiers connectedacross the said phase winding of said motor to which it correspondswhich is forward poled by the potential induced in the phase winding asthe magnitude of phase current flow in a second opposite directiontherethrough decreases.

1. In a cycloconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for eachsaid phase winding of said motor, two capacitors for each said phasewinding of said motor, two resistors for each said phase winding of saidmotor, means for connecting said anodecathode electrodes of one of saidsilicon controlled rectifiers in series with the parallel combination ofone of said capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, means for producing a gate signal when conduction througheach one of said phase windings of said motor is to be terminated, andmeans for applying said gate signal across said gate-cathode electrodesof the one of said silicon controlled rectifiers connected across thesaid phase winding of said motor through which conduction is to beterminated which is forward poled by the potential induced in the phasewinding as the magnitude of phase current flow therethrough decreases.2. In a cyclOconverter system for cyclically energizing the phasewindings of an alternating current induction motor from an alternatingcurrent supply potential source, a circuit for dissipating the potentialinduced in each phase winding of the motor upon the termination ofconduction therethrough comprising in combination with a cycloconvertercircuit made up of a network of cycloconverter silicon controlledrectifiers through which the phase windings of the motor are energizedand a cycloconverter silicon controlled rectifier gate switch forproducing a gate signal corresponding to each cycloconverter siliconcontrolled rectifier included in the network, two silicon controlledrectifiers, each having anode, cathode and gate electrodes, for eachsaid phase winding of said motor, two capacitors for each said phasewinding of said motor, two resistors for each said phase winding of saidmotor, means for connecting said anode-cathode electrodes of one of saidsilicon controlled rectifiers in series with the parallel combination ofone of said capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, a silicon controlled rectifier gate switch for producing agate signal when conduction through each one of said phase winding ofsaid motor is to be terminated, and means for applying said gate signalacross said gate-cathode electrodes of the one of said siliconcontrolled rectifiers connected across the said phase winding of saidmotor through which conduction is to be terminated which is forwardpoled by the potential induced in the phase winding as the magnitude ofphase current flow therethrough decreases.
 3. In a cycloconverter systemfor cyclically energizing the phase windings of an alternating currentinduction motor from an alternating current supply potential source, acircuit for dissipating the potential induced in each phase winding ofthe motor upon the termination of conduction therethrough comprising incombination with a cycloconverter circuit made up of a network ofcycloconverter silicon controlled rectifiers through which the phasewindings of the motor are energized and a cycloconverter siliconcontrolled rectifier gate switch for producing a gate signalcorresponding to each cycloconverter silicon controlled rectifierincluded in the network, two silicon controlled rectifiers, each havinganode, cathode and gate electrodes, for each said phase winding of saidmotor, two capacitors for each said phase winding of said motor, tworesistors for each said phase winding of said motor means for connectingsaid anode-cathode electrodes of one of said silicon controlledrectifiers in series with the parallel combination of one of saidcapacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, a first silicon controlled rectifier gate switchcorresponding to each said phase winding of said motor for producing agate signal when conduction in a first direction through the said phasewinding of said motor to which it corresponds is to be terminated, meansfor applying said gate signal produced by said first silicon controlledrectifier gate switch across said gate-cathode electrodes of the one ofsaid silicon controlled rectifiers connected across the said phasewinding of said motor to which said first silicon controlled rectifiergate switch corresponds which is forward poled by the potential inducedin the phase winding as the magnitude of phase current flow in a firstdirection therethrough deCreases, a second silicon controlled rectifiergate switch corresponding to each said phase winding of said motor forproducing a gate signal when conduction in a second opposite directionthrough the said phase winding of said motor to which it corresponds isto be terminated, and means for applying said gate signal produced bysaid second silicon controlled rectifier gate switch across saidgate-cathode electrodes of the one of said silicon controlled rectifiersconnected across the said phase winding of said motor to which itcorresponds which is forward poled by the potential induced in the phasewinding as the magnitude of phase current flow in a second oppositedirection therethrough decreases.
 4. In a cycloconverter system forcyclically energizing the phase windings of an alternating currentinduction motor from an alternating current supply potential source, acircuit for dissipating the potential induced in each phase winding ofthe motor upon the termination of conduction therethrough comprising incombination with a cycloconverter circuit made up of a network ofcycloconverter silicon controlled rectifiers through which the phasewindings of the motor are energized and a cycloconverter siliconcontrolled rectifier gate switch for producing a gate signalcorresponding to each cycloconverter silicon controlled rectifierincluded in the network, two silicon controlled rectifiers, each havinganode, cathode and gate electrodes, for each said phase winding of saidmotor, two capacitors for each said phase winding of said motor, tworesistors for each said phase winding of said motor, means forconnecting said anode-cathode electrodes of one of said siliconcontrolled rectifiers in series with the parallel combination of one ofsaid capacitors and one of said resistors and for connecting saidanode-cathode electrodes of the other said silicon controlled rectifierin series with the parallel combination of the other said capacitor andthe other said resistor across each said phase winding of said motorwith said silicon controlled rectifiers poled in an opposite polarityrelationship, a first silicon controlled rectifier gate switchcorresponding to each said phase winding of said motor for producing agate signal in response to each termination of the gate signal producedby any one of the said cycloconverter silicon controlled rectifier gateswitches corresponding to the said cycloconverter silicon controlledrectifiers which complete an energizing circuit in a first directionthrough the said phase winding of said motor to which it corresponds,means for applying said gate signal produced by said first siliconcontrolled rectifier gate switch across said gate-cathode electrodes ofthe one of said silicon controlled rectifiers connected across the saidphase winding of said motor to which it corresponds which is forwardpoled by the potential induced in the phase winding as the magnitude ofphase current flow in a first direction therethrough decreases, a secondsilicon controlled rectifier gate switch corresponding to each saidphase winding of said motor for producing a gate signal in response toeach termination of the gate signal produced by any one of the saidcycloconverter silicon controlled rectifier gate switches correspondingto the said cycloconverter silicon controlled rectifiers which completean energizing circuit in a second opposite direction through the saidphase winding of said motor to which it corresponds, and means forapplying said gate signal produced by said second silicon controlledrectifier gate switch across said gate-cathode electrodes of the one ofsaid silicon controlled rectifiers connected across the said phasewinding of said motor to which it corresponds which is forward poled bythe potential induced in the phase winding as the magnitude of phasecurrent flow in a second opposite direction therethrough decreases.